Intelligent hydraulic manifold used in an injection molding machine

ABSTRACT

Apparatus and method for controlling a hydraulic actuator in an injection molding machine, where the hydraulic actuator moves in a linear or rotary manner to effect movement of an injection molding device, such as a mold clamp. A microcontroller is locally disposed adjacent to the actuator or the hydraulic fluid distribution manifold to cause the actuator to drive the device. The microcontroller is electrically coupled to the system control processor. This distributed control architecture increases system processing throughput, enhances reliability, and permits easier upgrades/repair. Preferably, the microcontroller is mounted on the manifold and controls all of the actuators supplied from that manifold.

This is a divisional application of U.S. application Ser. No.09/173,732, filed Oct. 16, 1998, now U.S. Pat. No. 6,289,259.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an apparatus and methods forcontrolling a hydraulic actuator for use in an injection moldingmachine, and more particularly to controlling such a hydraulic actuator(both linear and rotary) with a processor which is disposed locally nearthe actuator and/or the hydraulic manifold.

2. Related Art

Injection molding machines produce great quantities of products at highspeed. For example, the widely-used PET plastic drink containers aremade at production rates of thousands per hour. During these high speedoperations, various injection molding machine devices (such as themolding clamp assembly, the injectors, various control switches, andother machine components) are moved using a number of hydraulicactuators. Such hydraulic actuators are supplied with pressurizedhydraulic fluid that causes movement of an internal diaphragm or pistonwhich, in turn, drives the molding device. A control valve controls theflow of hydraulic fluid to the actuator to control movement of thediaphragm. FIG. 1 depicts a typical control valve. In FIG. 1, thehydraulic actuator 2 includes a piston 4 which divides a chamber intotwo halves 6 and 8. Movement of the piston 4 drives a load 10, which,for example, may comprise a mold and clamp mechanism. A position sensor12 senses the position of the load 10 and provides a feedback signal toa system controller (to be discussed below).

The hydraulic actuator 2 has two hydraulic fluid lines 64 and 84 whichallow hydraulic fluid to enter and escape from the chamber halves 6 and8, respectively. Pressure transducers 66 and 86 respectively monitor thepressure in line 64 and 84 and provide output signals to the systemcontroller.

Hydraulic fluid from a pressure source (typically a hydraulic fluidpump; not shown in FIG. 1) is provided to valve 14 through hydraulicline 74, while hydraulic fluid may be returned from valve 14 tohydraulic fluid storage tank (also not shown in FIG. 1) throughhydraulic line 94. Pressure transducers 76 and 96 respectively monitorthe pressure in lines 74 and 94 and provide output signals to the systemcontroller.

Valve 14 controls the flow of hydraulic fluid through the chambers ofhydraulic actuator 2 to move the piston 4 back and forth thus drivingthe load 10. Valve 14 has fluid ports A, B, P, and T which arerespectively coupled to the hydraulic lines 64, 84, 74, and 94, asshown. The valve 14 has a straight flow section 142 and a cross-flowsection 144 which are respectively driven by solenoids 146 and 148 inorder to control the flow of fluid within the valve. For example, whenthe straight flow section 142 is driven to the A, B, P, and T ports,pressurized fluid will flow through lines 74 and 64 into chamber 6,driving the piston 4 toward the load 10. On the other hand, ifcross-flow section 144 is driven to the ports A, B, P, and T, thenpressurized hydraulic fluid will be provided through lines 74 and 84 tothe chamber 8, driving the piston 4 away from the load 10.

In the related art, control of the hydraulic actuator 2 through thevalve 14 was a relatively straightforward process. For example, U.S.Pat. No. 5,062,052 (incorporated herein by reference) discloses thatsuch actuators may be controlled with an analog signal processor and/ora programmable logic controller which are disposed at a location remotefrom the injection molding actuators so that the processing circuitry isnot damaged by machine heat and vibration. Typically, the analog signalprocessor and/or the programmable logic controller will performclosed-loop control of the actuator 2 through valve 14 in order to keepload 10 moving within the prescribed operational ranges. The analogsignal processor and/or programmable logic controller will receivefeedback signals from the pressure transducer units 66, 76, 86, and 96,and position information from position sensor 12 in order to controlvalve 14 according to a predetermined control program. The analog signalprocessor can also effect operational changes in the operation of theactuator 2 through command signals received through the programmablelogic controller, for example to change the molding and clamping timesused by load 10.

The programmable logic controller stores a plurality of predeterminedcontrol programs which cause the analog signal processor to control theanalog devices of the injection molding machine. The programmable logiccontroller may also include circuitry for controlling the digitaldevices in the injection molding machine, for example, digital solenoidvalves and proximity switches. The programmable logic controller thuscontrols the elements of the injection molding machine either throughthe analog signal processor or directly through the digital devices.

In the control scheme of the '052 Patent, however, the analog signalprocessor and the programmable logic controller are required to performcommand and control operations for all of the various devices in themachine. This imposes a processing bottleneck. For example, theprogrammable logic controller may attempt to execute closed-loop controlof multiple different analog devices at the same time. Typically, fasterand more powerful processors have been used in an attempt to overcomesuch problems. Such expensive solutions have, nevertheless, been unableto solve the control timing problems experienced in known actuatorcontrol architectures.

Another problem with the known control architecture is the reliabilityof the analog signal processor and the programmable logic controller. Ifeither one of these components fails, the entire machine must be stoppeduntil a replacement is located, installed, and programmed to operate inthe specified machine. Since each actuator in every machine has uniqueoperating characteristics, the newly-installed processor(s) must bere-programed and/or re-parameterized with the operating characteristicsof the corresponding actuator(s) before full-scale production can beresumed.

Furthermore, the dedicated wiring inter-connections used forcommunication between the analog signal processor and the programmablelogic controller to each actuator results in a plurality of wires whichare difficult to install, maintain, and repair.

Thus, a need exists for a control architecture for hydraulic actuatorsin an injection molding machine which provides fast, flexible, andreliable control of the actuators.

SUMMARY OF THE INVENTION

An object of the present invention is to overcome the problems notedabove by providing a local processor disposed near the actuator so thatcontrol functions are moved closer to the actuator and away from thecentral processor. Preferably, a microcontroller is mounted directly oneach hydraulic fluid distribution manifold, and this microcontrollercontrols the actuators coupled to that manifold. Each hydraulic actuatorcan be controlled from a local processor, eliminating the need for agreat number of wires between the actuator and the analog signalprocessor and/or the machine controller, such as a programmable logiccontroller. This enables modular control sub-systems to be realized.Also, a failure of any manifold-mounted microcontroller will onlyrequire its replacement, not the replacement of the central controlleror the other manifold microcontrollers.

According to a first aspect of the present invention an intelligenthydraulic actuator for use in an injection molding machine which alsohas a system controller includes a hydraulic actuator for moving in alinear or rotary manner between first and second positions, or forgenerating forces or torque in response to hydraulic flow and pressure,respectively. A microcontroller is disposed adjacent the actuator forcausing the actuator to move between the first and second positions. Themicrocontroller is also coupled to the system controller.

According to another aspect of the present invention, apparatus forcontrolling a hydraulic actuator in an injection molding machine having(i) a hydraulic manifold for supplying hydraulic fluid to the hydraulicactuator, (ii) a system control processor, and (iii) a sensor forsensing the operational conditions of the hydraulic actuator includes aprocessor which controls movement of the actuator. The processor has amemory for storing at least one control program which the processor runsto control the movement. The processor is mounted on the manifold. Acommand input provides command signals from the system control processorto the local processor, and a control output provides control signalsfrom the processor to a hydraulic valve, thus controlling the actuator.

According to yet another aspect of the present invention, an injectionmolding machine includes a plurality of molding devices which perform aninjection molding operation, and a system control processor for causingthe plurality of molding devices to perform the injection moldingoperation. A plurality of hydraulic actuators are provided forrespectively moving the plurality of molding devices, and a plurality ofvalves respectively provide hydraulic fluid to the hydraulic actuatorsto move the plurality of molding devices. A manifold provides hydraulicfluid to the plurality of valves. A processor is disposed adjacent atleast one of (i) the manifold, and (ii) at least one of the plurality ofvalves. The processor is coupled to each of the plurality of valves andto the system control processor. The processor stores a control programfor each of the plurality of hydraulic actuators coupled thereto, andthe processor controls the plurality of valves based on the storedcontrol programs and command signals received from the system controlprocessor.

In another aspect of the present invention, a method of controlling ahydraulic actuator which is supplied with hydraulic fluid from acontrollable valve and a manifold includes the steps of (i) disposing amicrocontroller adjacent the manifold, (ii) storing in themicrocontroller a control program for controlling a movement of thehydraulic actuator, (iii) providing to the microcontroller feedbacksignals from a sensor which senses a performance characteristic of thehydraulic actuator, (iv) providing to the microcontroller commandsignals from the system control processor, (v) calculating, in themicrocontroller, control signals to control the valve to cause themovement of the hydraulic controller, the microcontroller being capableof calculating the control signals based on one or more of the feedbacksignals, the command signals, and the stored control programs, and (vi)transmitting the control signals to the controllable valve.

According to a further aspect of the present invention, apparatus forcontrolling non-linear characteristics of a hydraulic actuator having avalve and a feedback sensor includes a memory for storingmulti-dimensional data regarding operational characteristics of thevalve, and a processor. The processor receives feedback signals from thefeedback sensor, determines operational data from the multi-dimensionaldata stored in the memory based on the received feedback signals,generates control signals by applying an inverse function to theoperational data in order to control for non-linear characteristics ofthe hydraulic actuator, and outputs the control signals to the valve.

A further aspect of the present invention involves apparatus forcontrolling a hydraulic actuator comprising a first valve coupled to theactuator and causing movement of the actuator by controlling movement ofhydraulic fluid through the valve, a second valve coupled to both thefirst valve and the actuator for causing movement of the actuator bycontrolling movement of hydraulic fluid through the first valve and thesecond valve, and a microcontroller, disposed adjacent to the valves,for controlling the first valve and the second valve to causeregenerative and non-regenerative control of the actuator.

An additional aspect of the present invention features at least onecomputer-readable storage medium storing an instruction set which causesa microcontroller to control a hydraulic actuator and an injectionmolding machine by performing the steps of: (i) storing a controlprogram which provides control signals based on feedback signals from atleast one sensor which monitor operational parameter(s) of the actuator,(ii) receives feedback signals from the sensor(s), (iii) receivescommand signals from an injection molding system control processor, (iv)modifies the stored control program based on the received commandsignals, (v) generates actuator control signals based on one of thestored control program and the modified stored program, and (vi) outputsthe actuator control signals to the actuator.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be more readily understood from a detaileddescription of the preferred embodiments taken in conjunction with thefollowing figures:

FIG. 1 is a schematic representation of a typical hydraulic actuator andvalve used in an injection molding machine;

FIG. 2 is a schematic block diagram of a first embodiment according tothe present invention;

FIG. 3 is a graph demonstrating proportional valve flow vs. strokeaccording to an embodiment of the present invention;

FIG. 4 is a graph demonstrating flow rate vs. demand according to anembodiment of the present invention;

FIG. 5 is a graph depicting flow rate vs. demand in an embodimentaccording to the present invention;

FIG. 6 is a graph depicting compensated flow rate vs. demand accordingto an embodiment of the present invention;

FIG. 7 is a schematic block diagram depicting a two-valve embodimentaccording to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

1. Introduction

The present invention will be described with respect to controllinghydraulic actuators (both linear and rotary) in an injection moldingmachine. However, the invention is not limited to injection moldingmachines and will solve actuator control problems in a wide variety ofapplications. For example, the fluid described below could be any knownliquid or gas useful in controlling an actuator. The scope of thepresent invention is to be ascertained from the appended claims and notthe detailed description of the preferred embodiments.

The present invention features a computer, processor, microcontroller,or microcontroller mounted on a hydraulic fluid manifold and/or actuatorto provide localized control, enhanced reliability, and reduced wiringin hydraulic actuator control systems. Mounting the processor on themanifold and/or actuator thus incorporates the processing and controlfunctionality of a process control unit in an integrated mechanicalassembly including hydraulic control valves with digital (on-offswitching), proportional and servo functions, and the correspondingvalve driver electronics, together with pressure transducers forpressure measurements and linear/rotary transducers for actuatorposition. Thus, a closed-loop control system can be realized locallywithout requiring system control resources. Apart from providing theprocessed control functions mentioned above, the on-board computerpossesses communication capability either through the discrete controlsignals (digital and/or analog) or a field bus which enables networkingthe local microcontroller to the system control processor and/or otherprocessors disposed within the factory. For field bus or device-levelnetworks, the local microcontroller can be decentralized via fiber opticcable(s), twisted wire pairs, or other communications means. Thedecentralized network capability offered by a field bus improves thecontrol system flexibility.

Incorporating the computer and communication capabilities of a processorat the local manifold and/or actuator, makes it possible to distributeintelligent process control as close as possible to the actuatorsthroughout the system. Such manifold-mounted processors having integralfield bus connectivity enable control to be decentralized throughout thesystem. The addition of the on-board intellegence (computation)capability of the local microcontroller provides local control of thesub-system. This enables proprietary control techniques and processknowledge to be utilized, yet be open for easy connection to othersub-systems for system integration. Proprietary control techniques suchas flow rate linearization (to be discussed below) and dynamic spool cutadaptation (also to be discussed below) can be migrated to the localizedon-board computer. In addition, the on-board computer providesadditional diagnostics to the components of the local sub-system, anddata acquisition for quality control and monitoring. The on-boardcomputer reduces the complexity of the system control processor andenhances the modularity of the system. Now, when problems occur in onelocal sub-system, it is not necessary to take the whole machine off-lineand re-configure the entire control system. Instead, the localmicrocontroller can be replaced and/or reprogrammed to rapidly overcomethe sub-system problem and return the machine to full production.

The preferred embodiment incorporates an on-board microcontrollermounted on a hydraulic manifold which supplies hydraulic fluid to aplurality of valves which, in turn, are coupled to a plurality ofhydraulic actuators. Communication of control and feedback informationbetween the manifold and the system control processor can be carried outwith discrete input and output signals in analog or digital form. Astandardized industrial fieldbus can also be incorporated to enhancecommunication with reduced connections. With a single communicationpoint for each sub-system, the overhead to support multiple fieldbusdevices is greatly reduced which results in higher response controlsfrom the control system. The hydraulic manifold thus becomes an“intelligent” manifold which can perform functions which would not bepossible otherwise. Since the processing power demanded from the systemcontrol processor is reduced, an overall improvement in systemperformance and speed is realized. When a fieldbus is used to connectthe manifold microcontroller to the system control processor, the systemcost for complex manifolds with multiple devices is significantlyreduced. The local control of the manifold sub-system thus enablesfactory calibration and performance characteristic curves for everyindividual device to be stored in the memory of the on-boardmicrocontroller. This allows additional fine-tuning of the localsub-systems by advanced control strategies and algorithms which, forexample, may linearize the feedback from the measurements of thetransducers and the control elements. In addition, change of componentsmay be realized by merely revising the data stored in themicrocontroller. This can be done by loading into the microcontrollerone or more software programs stored on one or more computer-readablestorage mediums such as diskettes, CD-ROMs, tapes, pre-programmedmicrocontrollers, EEPROMs, optical-magneto devices, etc. The programsmay be loaded into the microcontroller from the system controller,through a network connection, or directly into the localmicrocontroller.

2. The Structure of the Preferred Embodiment

FIG. 2 is a schematic block diagram of one structure according to thepreferred embodiment in which the same structure as discussed above withrespect to FIG. 1 is depicted with the same reference numerals. In FIG.2, a hydraulic manifold 202 receives pressurized hydraulic fluid from apressure source (e.g. a pump, or an accumulator and pump) 204, andreturns hydraulic fluid to a tank 206. Hydraulic pressure and returnlines extend from the manifold 202 to various valves which operatedifferent hydraulic actuators. In FIG. 2, the manifold 202 providespressurized and returned hydraulic fluid to the valve 14 discussed abovein FIG. 1.

The microcontroller 210 is in close proximity (e.g. within one meter) tothe manifold 202 to control the operations of the valve 14, and thus theactuator 2. The microcontroller 210 may also control the other valvesand actuators coupled to the manifold 202. While FIG. 2 depicts themicrocontroller 210 mounted on the manifold 202, the microcontroller maybe mounted adjacent the valve 14 or the actuator 2. So long as themicrocontroller is mounted locally, the processing advantages achievedby the present invention can be realized.

As shown in FIG. 2, the microcontroller 210 is coupled to the pressuretransducers 66, 76, 86, and 96 to monitor the pressure going into andcoming out of the valve 14. The microcontroller 210 also receivesposition information from the position sensor 12 coupled to the load 10.The microcontroller 210 may also receive feedback signals from othersystem sensors which monitor various operational characteristics of thehydraulic actuators to be controlled by the microcontroller.Accordingly, the microcontroller 210 can execute closed-loop control ofthe actuator 2 through control of the valve 14. In particular, themicrocontroller 210 has a ROM (not shown) and a RAM (also not shown)which store one or more control programs which the microcontroller 210executes to control the solenoid drivers 146, 148 of the valve 14. Sincethe microcontroller 210 contains all necessary programs and receives allnecessary feedback, control can be executed without reference to thesystem control processor 216. The microcontroller 210 will providefeedback, status, and operational information to the system controller216 which, in turn, can command the microcontroller 210 to switchcontrol programs or to modify the programs being executed. When the newcontrol programs are desired to be installed in the microcontroller 210,these can be installed locally at the manifold, or can be installedthrough the system control processor 216.

The microcontroller 210 preferably includes D/A and A/D circuitry sothat it can locally control both digital and analog drivers required bythe sub-system hydraulic actuators.

The microcontroller 210 can be any commercially availablemicrocontroller for embedded controls processor such as a Pentium IIprocessor with one Gigabyte ROM and 64 MB of RAM. The microcontrollermay also be termed a microprocessor, a computer, a processor, or otherterms known to those of skill in the injection molding art. However, theterm microcontroller is preferred due to its meaning in this art.

The system control processor 216 performs overall process control forthe injection molding machine and schedules control signals to besupplied to the microcontroller 210. Such signals may include those forcalculating the minimum output to a valve based on a velocity profilewith a pressure limit. The system control processor 216 may receivefeedback information from the microcontroller 210 and/or the positionsensor 12. This information may include actual pressure, currentposition, etc. The system control processor 216 also receivesinformation from a human machine interface, such as an operator-setvelocity profile, pressure limits, temperature set points, etc. Suchinformation is provided to the microcontroller 210 which then decides onthe correct outputs to the solenoid valve drivers 146 and 148.

The control architecture depicted in FIG. 2 provides great flexibilityin controlling the injection molding machine. Actuator control functionscan reside in the microcontroller 210 and/or the system controlprocessor 216. In a machine with a great number of sub-systems, most ofthe control functions will be migrated to the individualmicrocontroller(s) 210. In machines with fewer sub-systems, the systemcontrol processor 216 may carry out some of the machine controlfunctions.

The microcontroller 210 can be installed in a relatively simple systemwith a single valve, with the microcontroller storing minimal controlprograms for controlling a single actuator. Or, the microcontroller 210can be installed as a sophisticated control controlling multiple valves,multiple axes of control, and store control programs for each actuator,as well as control programs for synchronizing the operation of all ofthe sub-system actuators. The microcontroller 210 may store controlprograms such as: valve displacement vs. flow at a given pressure drop;integrated processing and scheduling power for each actuator;closed-loop pressure and/or force control with integrated pressuretransducers; so-called “sanity” checks, for example, actuator velocitywith respect to position information from the position sensor 12;defined interface protocol; individualized actuator strokes (linear),areas (linear), and geometric displacements (rotary); inferred friction,natural frequency, etc.; and physical limits (displacement limits,velocity limits, acceleration limits, jerk limits, force limits,pressure limits, rate of pressure change limits, etc.).

The microcontroller 210 may, in fact, be standardized for any manifoldcontrolling a simple actuator, such as that depicted in FIG. 2. Thecontrol program may be identical for different sizes of valves andactuators, and only the initialization parameters (actuator and valveinformation) need to be input at the start-up period.

Preferably, the connection between the system control processor 216 andthe microcontroller 210 is a fieldbus 218. This is a bi-directional buswhich may comprise optical cable, a twisted pair, or other suitablecommunications means. The field bus is capable of handling high speedinformation exchange and can thus provide real-time control between thesystem control processor 216 and the microcontroller 210. The systemcontrol processor 216 can send control signals to the microcontroller210 such as to initiate process signals, scheduling signals, controlprograms updates, etc. In turn, the microcontroller 210 can sendfeedback signals to the system control processor 216 such as valvestatus, pressure levels, position sensor status, stored reliabilityinformation, etc.

3. Non-Linear Compensation

Hydraulic actuators possess non-linear characteristics such as change inhydraulic stiffness due to the change in oil volume between the valveand the cylinder piston and pressure-dependent flow, but the actuatorshould be operated in the linear region for effective parameter control.For example, the non-linear characteristics can lead to loss of controlor even closed-loop instability. By providing increased processing poweradjacent the hydraulic manifold, it is possible to compensate for thenon-linear characteristics of each hydraulic actuator to ensure reliableoperation. The microcontroller 210 can store a control program whichcompensates for such non-linear characteristic and ensures linearcontrol of the hydraulic actuator. Referring to Diagram A below, thecompensation method according to the present invention will compensatefor the main nonlinearity if by an approximate inverse function f⁻¹,which can be implemented in the controller. According to Diagram A, theregular actuator input U is then substituted by the “corrected” valuesuch that the relationship between U and y becomes approximately linear.Here G_(A) represents the dynamics of the control valve, G_(p) themechanical system, and x the process states and variables.

The nonlinear relation f⁻¹ follows from:U ^(c) =U·f ⁻¹(x)  (1)x ₂ =U ^(c) ·K _(A) ·f(x)  (2)andx ₂ =K·U  (3)where K describes the determined gain of the linearized system and K_(A)describes the gain of the input system G_(A). The dynamics of the valve,G_(A), are often negligible compared with the time constants of G_(P)(control valve versus mechanical system dynamics). If f(x) could offer aprecise approximation, good and robust compensation results would beobtained.Flow Rate Linearization

Consider the sharp edge orifice's relationship:q _(l) =k _(v) ·a(x _(v))·√{square root over (p _(s) −p _(l))}  (4)where:

-   q_(l)=Load Flow $\begin{matrix}    {k_{v} = {{{Valve}\quad{Coefficient}} = {C_{d} \cdot \sqrt{\frac{2}{\rho}}}}} & (5)    \end{matrix}$  a(x _(v))=Orifice Area For a Given Valve Stroke    Position x_(v)-   p_(s)=Supply Pressure-   p_(l)=Load Pressure-   C_(d)=Valve Flow Characteristic-   ρ=Fluid Density    Single Valve/Single Axis/Minimum Self Knowledge/Minimum Axis    Knowledge

The valve characteristic of flow vs. valve stroke at a fixed pressuredrop (see FIG. 3) resides in the Intelligent Manifold Controller. Thischaracteristic is used to calculate the actual flow through thecontrolling valve by determining what the current pressure drop is andscaling the valve characteristic pressure drop to the actual pressuredrop using the following formula: $\begin{matrix}{Q_{actual} = {Q_{characteristic} \cdot \sqrt{\frac{\Delta\quad P_{actual}}{\Delta\quad P_{characteristic}}}}} & (6)\end{matrix}$

Equation 4 can be rewritten as: $\begin{matrix}{q_{1} = {{k_{v} \cdot {a\left( x_{v} \right)} \cdot \sqrt{r \cdot p_{s}} \cdot \sqrt{\frac{p_{s} - p_{1}}{r \cdot p_{s}}}} = {k_{v} \cdot {a\left( x_{v} \right)} \cdot \sqrt{r \cdot p_{s}} \cdot {f\left( p_{x} \right)}}}} & (7)\end{matrix}$with

r=Compensation Ratio

f(p_(x))=Pressure Valve For Spool Position x

p_(x)=f(p_(s), p_(l))and by selecting an inverse function: $\begin{matrix}{{f^{- 1}\left( p_{x} \right)} = \sqrt{\frac{r{\cdot p_{s}}}{p_{s} - p_{1}}}} & (8)\end{matrix}$the compensated flow will have the following relationship:q _(l) ^(c) =k _(v) ·a(x _(v))√{square root over (p _(s) −p _(l))}·f⁻¹(p _(x))=k _(v) ·a(x _(v))√{square root over (r·p _(s))}  . . . (9)

The parameter r provides a means to adjust the flow gain of the valve.The flow gain of the valve is limited by the system pressure and maximumarea opening of the orifice. The following flow characteristic curveshelp to illustrate the effects of the compensation based on different rvalues.

FIG. 4 is a graph depicting the uncompensated flow rate versus demand.By increasing the value of r, the flow gain could be increased until thesaturation limit is reached. With a value of r larger than 0.5, flowgain starts to show nonlinear behavior due to valve saturation, for p₁at greater than half the supply pressure. For proper performance, thevalue of r is limited to 1.

FIG. 5 depicts compensated flow rate versus demand for r=0.5. FIG. 6shows compensated flow rate versus demand where r=1.

4. Dynamic Spool Cut Tuning

A single valve controlling an axis has a fixed relationship between theconnection of each valve port (i.e. P, T, A, and B), since the spool isone piece. Currently, the spool cut (the cut of the orifices leadinginto the chambers) is typically tuned to the ratio of the cylinder (i.e.2:1, 10:1, etc.). This fixed opening ratio works well for the case ofconstant velocity, but there is currently no way to adjust the ratio ofthe valve opening after the system is constructed.

A solution to this problem is to use two three way (P, T, and A)proportional (servo) valves (FIG. 7, valve 72 and valve 74). Thesevalves in conjunction with pressure transducers 66, 76, 86, and 96 inthe P, T, and A ports of the valves 72, 74 allow profiling the pressureor flow into and out of the actuator cylinder (this could also be arotary actuator). This system may be used to:

-   1. Operate an axis regeneratively (i.e., return hydraulic fluid from    one valve to another) under some situations and non regeneratively    (fluid is returned to the storage tank) for other situations.-   2. Profile the pressure in the actuator to get the optimum    acceleration, velocity, force control, deceleration, jerk, etc. for    the system.

TABLE 1 Sequence Chart Function Valve 74 Valve 72 Rod Extend High SignalLow Signal (non (P to Cylinder) (Cylinder to Tank) regenerative) RodExtend High Signal High Signal (regenerative) (P to Cylinder) (Cylinderto P) Rod Retract Low Signal High Signal (Cylinder to T) (P to Cylinder

This embodiment creates an additional degree of freedom for axiscontrol. This embodiment can seamlessly adjust the orifice metering inand/or metering out hydraulic fluid (oil) from each side of the cylinderindependent of what the other valve is doing. The additional degree ofcontrol freedom eliminates the requirements of a specially designedspool cut for a single control valve.

This embodiment also dynamically adjusts the valve openings based on therequired flow to the axis and the supply and load pressures. Thiscontrol is done locally (at the manifold microcontroller) and does notcreate any processing overhead to the system controller. The complexityof the control algorithm is transparent to the other parts of thesystem. The combined assembly can be considered as a single valve withan optimum spool cut design for any application.

5. Additional Embodiments

An intelligent manifold with embedded microcontroller permits themicrocontroller to learn about the system that it is attached to, and tostore such characteristic information for more precise control of theactuator. Some examples of such stored learning include:

-   -   The static and dynamic friction of the axis, and how the dynamic        friction changes with velocity, position and/or over time;    -   Changes in the friction values from the last time the system was        operated;    -   Changes in the trend of axis friction over time; (this allows        for adjustments in the control system and for predictive        maintenance to be used)    -   The effective axis mass, and any changes over time; and    -   Natural frequency of axis at different positions (oil volume,        mass).

Also, the local microcontroller may store additional operationalparameters to further enhance precision. These parameters may beprovided to the system controller for use therein in system wideoperational control. For example, the following parameters may bedetermined by the local microcontroller and stored therein and/or sentto the system controller:

-   -   Actuator displacement limit;    -   Actuator velocity limit;    -   Actuator acceleration profile;    -   Actuator jerk limit;    -   Pressure limits;    -   Rate of pressure change profile; and    -   Rate of pressure change limit.

Furthermore, the following local microcontroller-generated parametersmay be stored in the microcontroller and transmitted to the systemcontroller for the operator to use in operation of the injection moldingmachine:

-   -   Actuator displacement;    -   Velocity profile & force limit;    -   Force profile & velocity limit; and    -   Acceleration profile.

The following Tables A and B list some of the actuator and/or systemparameters which may be controlled by the local microcontroller disposednear the actuator.

TABLE A System Parameters What? Symbol Current Art Problem Displacementx Magnetostrictive None Device Velocity (flow)$\frac{\mathbb{d}x}{\mathbb{d}t}$ Magnetostrictive Device PLCcalculation of time rate of change of displacement Differentiationcreates noisy signal PLC differentiation creates time delay Acceleration$\frac{\mathbb{d}x^{2}}{\mathbb{d}t^{2}}$ Magnetostrictive Device PLCcalculation of time rate of change of velocity Differentiation createsnoisy signal PLC differentiation create time delays Hard to calculate online Jerk $\frac{\mathbb{d}x^{3}}{\mathbb{d}t^{3}}$ MagnetostrictiveDevice PLC calculation of time rate of change of accelerationDifferentiation creates noisy signal PLC differential creates timedelays Hard to calculate on line Pressure P Pressure None transducerForce Pressure × Area Pressure None (pressure) transducer PLCcalculation Force Mass × μ None for on N/A (friction) line Wear N/A Nonefor on N/A line Preventative N/A None for on N/A Maintenance lineDiagnostics N/A None for on N/A line System N/A None for on N/Aidentification line

TABLE B Velocity and Force Limits a Velocity e (flow) Force (pressure)Comment 0 0 Position Control without a Force limit. External force willmove axis to a new position 0 < F < System Position Control with a ForceLimit limit External force above a certain level will move axis to a newposition System Limit Position Control with out a Force limit Externalforce will not move axis. Positional restraining force limited by thecapability of the axis $\quad\begin{matrix}{0 < \frac{\mathbb{d}x}{\mathbb{d}t} <} \\{{System}\quad{Limit}}\end{matrix}$ 0 0 < F < System Limit Velocity Control Velocity ControlSystem Limit Velocity Control 0 Force Control System 0 < F < SystemForce Control Limit Limit System Limit Force Control6. Conclusion

Thus, what has been described is an intelligent hydraulic manifold withlocal processor control to distribute the control functions closer tothe controlled units, improve system processing performance, enhancereliability, provide greater system flexibility for upgrades/repairs,and reduce system downtime.

While the present invention has been described with respect to what arepresently considered to be the preferred embodiments, it is to beunderstood that the invention is not limited to the disclosedembodiments. To the contrary, the invention is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the following claims. The scope of the following claims is toaccorded the broadest interpretation so as to encompass all suchmodifications and equivalent structures and functions.

1. Apparatus configured for controlling a hydraulic actuator in aninjection molding machine having a system control processor performingoverall process control of the injection molding machine, said apparatuscomprising: a microcontroller configured to control the operation of ahydraulic control valve that regulates a supply of hydraulic fluid tothe hydraulic actuator to control movement thereof, the microcontrollerbeing remotely located from the system control processor and responsiveto command signals from the system control processor, the commandsignals received by the microcontroller being configured to cause localcontrol of the hydraulic control valve, said microcontroller generatingcontrol signals for communication to the hydraulic control valve inresponse to the command signals; a communications link configured toconnect said microcontroller to the system control processor and to thehydraulic control valve, the communication link being configured tocarry bi-directional communications; a sensor configured to monitor thehydraulic actuator and send, in response to an operational condition ofthe hydraulic actuator, feedback signals to the microcontroller; and amemory associated with the microcontroller and configured to store acontrol program, said command signals, and said and feedback signals,said memory also being configured to store operating characteristics ofat least one of said hydraulic control valve and said hydraulicactuator, said microcontroller being configured to use the storedoperating characteristics locally in said control program to generatecontrol signals that perform closed-loop control of the hydraulicactuator.
 2. The apparatus according to claim 1, wherein saidmicrocontroller is configured to operate a control program that uses thestored operating characteristics and feedback signals to (i) compensatefor a non-linear characteristic of the hydraulic actuator, and (ii)generate compensated control signals that provide substantially linearoperational control of the hydraulic control valve.
 3. The apparatusaccording to claim 1, further comprising a plurality of pressure sensorscoupled to the hydraulic control valve and configured to (i) monitorpressure going into and coming out of the hydraulic control valve, and(ii) generate a pressure feedback signal that is provided to themicrocontroller.
 4. The apparatus according to claim 3, wherein saidstored characteristics correspond to hydraulic fluid flow vs. hydraulicvalve stroke at a predetermined pressure drop, and wherein saidmicrocontroller is configured to execute a control program, stored inthe memory, that references said pressure feedback signals and saidstored characteristics to calculate a compensated flow rate using flowrate linearization, said microcontroller providing the compensated flowrate to the hydraulic control valve as a control signal configured toperform control of the hydraulic actuator.
 5. The apparatus according toany one of claims 1 and 2, wherein said stored characteristicscorrespond to at least one of: static and dynamic friction of a machinecontrol axis; a natural frequency of a machine control axis at differentpositions of the hydraulic actuator; and operational parametersdetermined by the local microcontroller.
 6. The apparatus according toany one of claims 3 and 4, wherein said hydraulic control valvecomprises first and second proportional valves configured to control theflow of hydraulic fluid through a pair of hydraulic lines coupled to thehydraulic actuator, and wherein said microcontroller uses feedbacksignals from the pressure sensor to control said first and secondproportional valves to provide regenerative and non-regenerative controlof said hydraulic actuator, whereby the pressure or flow of thehydraulic fluid into and out of the hydraulic actuator can be profiled.7. The apparatus according to claim 6, wherein said microcontroller isconfigured to control said first and second proportional valves toindependently adjust an orifice which meters hydraulic fluid into andout of each side of the hydraulic actuator.
 8. The apparatus accordingto claim 6, wherein said microcontroller is configured to dynamicallycontrol the opening of said first and second proportional valves basedon the required flow to the hydraulic actuator and the supply and loadpressures.
 9. The apparatus according to claim 1, wherein saidmicrocontroller is coupled to at least one of: a hydraulic manifoldconfigured to supply hydraulic fluid to said hydraulic actuator; saidhydraulic actuator; and said hydraulic control valve.
 10. An injectionmolding machine including the apparatus of claim
 1. 11. A method ofcontrolling a hydraulic actuator in an injection molding machine having(i) a system control processor, and (ii) a hydraulic control valve thatregulates a supply of hydraulic fluid to a hydraulic actuator,comprising the steps of: storing in a microcontroller, which is disposedremotely from the system control processor, a control program forcontrolling a movement of the hydraulic actuator; storing in themicrocontroller characteristic information corresponding to at least oneof (i) the hydraulic control valve, and (ii) the hydraulic actuator;providing to the microcontroller, and storing in a memory coupled to themicrocontroller, feedback signals from at least one sensor which sensesa performance characteristic associated with the hydraulic actuator;providing to the microcontroller, and storing in said memory, commandsignals from the system control processor; said microprocessor using (i)said stored control program, (ii) said stored characteristicinformation, (iii) said stored command signals, and (iv) said storedfeedback signals, to calculate control signals to control the hydrauliccontrol valve; and said microcontroller transmitting said controlsignals to the hydraulic control valve to cause movement of thehydraulic actuator.
 12. The method according to claim 11, furthercomprising the step of: said microcontroller transmitting said storedfeedback signals from said microcontroller to the system controlprocessor.
 13. The method according to claim 11, wherein said hydrauliccontrol valve comprises first and second proportional valves configuredto control the flow of hydraulic fluid through a pair of hydraulic linescoupled to the hydraulic actuator, and further comprising the steps of:said microcontroller calculating control signals for the first and saidsecond proportional valves; and said microcontroller transmitting saidcontrol signals to the first and said second proportional valves. 14.The method according to claim 13, wherein said microcontroller controlssaid first and second hydraulic control valves to provide regenerativeand non-regenerative control of said hydraulic actuator.
 15. The methodaccording to claim 11, further comprising the steps of: saidmicrocontroller calculating control signals for a plurality of hydraulicactuator valves; and said microcontroller transmitting said controlsignals to said plurality of hydraulic actuator valves.
 16. The methodaccording to any one of claims 11, 13, 14, and 15, wherein saidmicrocontroller controls said hydraulic control valve to linearizenon-linear characteristics of said hydraulic actuator.